Her heart undergoes several adverse age-related changes that lead to loss of performance and ultimately to heart failure, the major cause of death for people over the age of 65 in the U.S. Oxidative damage, loss of energy supply, and tissue atrophy are thought to be underlying factors causing cardiac dysfunction with age, which in turn are likely caused by mitochondrial decay. However, little is known about the extent or nature of mitochondrial decay in the aging heart and whether dietary supplements that ameliorate mitochondrial decline improves cardiac function. Some studies on mitochondrial decay have been performed using isolated mitochondria, but results are conflicting and difficult to interpret. This is primarily due to a technical problem: extensive mitochondrial lysis and damage during isolation from aged tissue. We proposed to characterize and compare mitochondrial function in intact freshly isolated cardiac myocytes from old and young rats. Advances in methodology now make analysis of mitochondrial function within intact cells feasible, and we now have preliminary evidence that mitochondrial decay occurs in isolated cardiac myocytes from old rats. Advances in methodology now make analysis of mitochondrial functions within intact cells feasible, and we now have preliminary evidence that mitochondrial decay occurs is isolated cardiac myocytes from old rats. Thus, the questions to be addressed in this proposal are A) what is the nature and extent of mitochondrial decay in cardiac myocytes with age? B) does mitochondrial decay affect cardiac function? C) does feeding old rats acetyl-L-carnitine (ALCAR) and (R)-lipoic acid (LA), compounds that we showed to enhance mitochondrial function and quench mitochondrial oxidants in isolated hepatocytes, also improve mitochondrial function in cardiac myocytes? We propose to investigate these questions in 3 specific aims: 1) Characterize and compare mitochondrial functions in isolated cardiac myocytes form young, adult, mature and old rats. Characterization will include oxygen consumption characteristics, bioenergics, and cardiolipin content in quiescent cells and in myocytes stimulated to contract. Other studies using isolated cardiac myocytes or isolated perfused hearts will determine the consequences of mitochondrial decay to cardiac performance. 2) Examine age-related changes in mitochondrial antioxidants, oxidant production, and myocardial oxidative damage. These studies will be instrumental in determining not only the impact of mitochondrial decay on oxidant production, but also the effect of mitochondrial production on the cell as a whole. 3) Assess whether feeding rats ALCAR and/or LA improves mitochondrial function, lowers oxidative stress in cardiac myocytes and improves cardiac performance. These experiments will measure the same experimental end-points as in specific aims 1 and 2. This project will thus be the first step in our long term goals of determining the importance of mitochondrial decay in pathologies of the aging human heart and whether dietary regimens that improve mitochondrial performance can be inexpensive yet effective therapies for cardiac dysfunction in aging.